Civil Engineeringhttp://hdl.handle.net/10539/11188
Sat, 10 Dec 2016 03:08:12 GMT2016-12-10T03:08:12ZReflections on future needs in concrete durability research and developmenthttp://hdl.handle.net/10539/11242
Reflections on future needs in concrete durability research and development
Ballim, Y.; Alexander, M.G.; Beushausen, H.D; Moyo, P.
There is no doubt that, over the past two decades, we have made enormous advances in the understanding and practice of concrete durability. Spurred by the often experienced early deterioration of reinforced concrete structures, with high capital investment for repair and rehabilitation, conceptions of design for durability have gained an increasingly higher level of importance in recent years.
It is not difficult to recognise or to acknowledge the significant changes that have taken place in the field of concrete durability over the last 25 years.
Fri, 03 Feb 2012 00:00:00 GMThttp://hdl.handle.net/10539/112422012-02-03T00:00:00ZEffectiveness of the fi neness of two South African Portland cements for controllingearly-age temperaturedevelopment in concretehttp://hdl.handle.net/10539/11199
Effectiveness of the fi neness of two South African Portland cements for controllingearly-age temperaturedevelopment in concrete
Graham, P.C.; Ballim, Y.; Kazirukanyo, J.
In developing an assessment of the quantum and rate of heat evolution from hydrating cement, an important controllable variable is the fineness of grinding of the cement. This paper presents the results of a project in which two cement clinkers were used to produce cements with five different levels of fineness. These ten cements were then used to make concretes which were subjected to testing in an adiabatic calorimeter to determine the heat evolution characteristics. The results indicate that the effect of increasing fineness on the total amount of heat released during hydration is dependent on the mineralogy and crystal composition of the cement clinker. Also, the potential benefits of a so-called low heat cement can be lost if the cement is too finely ground. Based on simulations of temperature development using the different cement types tested, the results indicate that the fineness of grinding of cement is a more important parameter in the case of concrete elements with high cement contents but of moderate dimensions. In sections of larger dimension, coarse ground cements show lower levels of temperature development with lower thermal gradients.
It is generally agreed that, for a given Portland cement, the rate and amount of heat liberated during the early stages of hydration (up to 28 days) is strongly influenced by the fineness of grinding of the cement (see review by Hooton et al 2005). This is intuitively correct since finer grinding means that the hydration reac¬tions between cement and water will proceed more vigorously at early ages and hence pro¬duce more heat and at a higher maximum rate. However, as Hooton et al (2005) show, opin¬ions vary in the literature as to the sensitivity of the relationship between cement fineness and early-age heat of hydration. Furthermore, when considering different cement types, the significance of the fineness of the cement has to be judged in relation to mineralogical parameters, such as the C3A, C3S and gypsum content, equally important factors in deter¬mining the heat characteristics of cement.
Fri, 01 Apr 2011 00:00:00 GMThttp://hdl.handle.net/10539/111992011-04-01T00:00:00ZThe effects of supplementary cementing materials in modifying the heat of hydration of concretehttp://hdl.handle.net/10539/11198
The effects of supplementary cementing materials in modifying the heat of hydration of concrete
Ballim, Yunus; Graham, Peter C.
Supplementary cementing materials, such as ground granulated blastfurnace slag(GGBS), fly ash (FA) and condensed silica fume (CSF), are now routinely used in structural concrete. Used judiciously, these materials are able to provide improvements in the economy, microstructure of cement paste as well as the engineering properties and durability of concrete. They also alter the rate of hydration and can influence the time-temperature profile in large concrete elements.
Tue, 23 Sep 2008 00:00:00 GMThttp://hdl.handle.net/10539/111982008-09-23T00:00:00ZDeterioration Presentationhttp://hdl.handle.net/10539/11196
Deterioration Presentation
Ballim, Y
Mon, 30 Jan 2012 00:00:00 GMThttp://hdl.handle.net/10539/111962012-01-30T00:00:00Z